US5048939AExpiredUtility

Zoom lens system

42
Assignee: HITACHI LTDPriority: Apr 21, 1989Filed: Apr 17, 1990Granted: Sep 17, 1991
Est. expiryApr 21, 2009(expired)· nominal 20-yr term from priority
Inventors:Masahiko YatsuMasaharu DeguchiTakesuke MaruyamaHironobu SatohKenji KobayashiKenji Sano
G02B 15/00G02B 15/17G02B 15/145125
42
PatentIndex Score
10
Cited by
1
References
11
Claims

Abstract

A zoom lens system comprises, from an objective sequentially, a first lens group (1) having a positive power, a second lens group and a third lens group (2) and (3) having negative power and performing a zooming function by moving along an optical axis, a fourth lens group (4) having a positive power and being always stationary, and a fifth lens group (5) having a positive power and having a triplet structure including, from an object side sequentially, a first lens (9) having a positive power, a second meniscus lens (10) having a negative power and a third lens (11) having a positive power, the fourth lens group including a lens at least one surface of which is aspherical, the first or the fifth lens group being movable as a whole or partially along an optical axis to perform a focusing function. The first, second and third lens groups satisfy the following conditions: 2.7<|f.sub.I /f.sub.II |<3.6 1.0<|f.sub.I /f.sub.III |<1.9 3.8<f.sub.I /f.sub.W <4.9 where f I is a focal length of the first lens group, f II is a focal length of the second lens group, f III is a focal length of the third lens group, and f W is a focal length of the whole system at a wide-angle end of the zoom lens.

Claims

exact text as granted — not AI-modified
What is claimed is: 
     
       1. A zoom lens system comprising, from an objective sequentially, a first lens group having a positive power, a second lens group and a third lens group both having negative powers and performing a zooming function by moving along an optical axis, a fourth lens group having a positive power and being always stationary, and a fifth lens group having a positive power and having an image forming function, said fourth lens group including a lens at least one surface of which is aspherical, said first lens group being movable as a whole or partially along an optical axis to perform a focusing function. 
     
     
       2. The zoom lens system claimed in claim 1, wherein said fifth lens group comprises, from an object side sequentially a first lens having a positive power, a second meniscus lens having a negative power, and a third lens having a positive power. 
     
     
       3. The zoom lens system claimed in claim 1 or 2, wherein said first lens group said second lens group, and said third lens group satisfy the following conditions:   2,7<|f.sub.I /f.sub.III |<3.6       1.0<|f.sub.I /f.sub.III |<1.9       3.0<f.sub.I /f.sub.W <4.9     where f I  is a focal length of said first lens group, f II  is a focal length of said second lens group, f III  is a focal length of said third lens group, and f W  is a focal length of the whole system at a widest zoom lens angle.   
     
     
       4. The zoom lens system claimed in claim 2, wherein said second meniscus lens of said fifth lens group has meniscus-shaped surface having a large curvature on the image side. 
     
     
       5. A zoom lens system comprising, from an objective sequentially, a first lens group having a positive power, a second lens group and a third lens group both having negative powers and performing a zooming function by moving along an optical axis, a fourth lens group having a positive power and being always stationary, and a fifth lens group having a positive power, said fourth lens group including a lens at least one surface of which is aspherical, said fifth lens group being movable as a whole or partially along an optical axis to perform a focusing function. 
     
     
       6. The zoom lens system claimed in claim 5, wherein said fifth lens group comprises, from an object side sequentially, a first lens having a positive power, a second meniscus lens having a negative power, and a third lens having a positive power. 
     
     
       7. The zoom lens system claimed in claim 5 or 6, wherein said fourth lens group (4) and said fifth lens group satisfy the following condition:   0.13<d.sub.IV,V /f.sub.V <0.23     were d IV ,V is a distance on an optical axis between a surface of said fourth lens group closest to the focal plane and a surface of said fifth lens group closest to the object when a photographing distance to the object is infinite, and f V  is a focal length of said fifth lens group.   
     
     
       8. The zoom lens system claimed in claim 5, wherein said fifth lens group includes a lens having at least one surface which is aspherical. 
     
     
       9. The zoom lens system claimed in claim 6, wherein said third lens of said fifth lens group (5) has at least one surface which is aspherical. 
     
     
       10. The zoom lens system claimed in claim 5 or 6, wherein said first lens group, said second lens group, and said third lens group satisfy the following conditions:   2.7<|f.sub.I /f.sub.II |<3.6       1.0<|f.sub.I /f.sub.III |<1.9       3.8<f.sub.I /f.sub.W <4.9     where f I  is a focal length of said first lens group, f II  is a focal length of said second lens group, f III  is a focal length of said third lens group, and f W  is a focal length of the whole system at a widest zoom lens angle.   
     
     
       11. The zoom lens system claimed in claim 6, wherein said second meniscus lens of said fifth lens group has meniscus-shaped surface having a large curvature on the image side.

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